Basic Interpretation of an Electrocardiogram (ECG) Flashcards
What does an ECG measure?
- Rate
- Rhythm
- Time-dependent vector of the heart
- Origin of cardiac action potential
- Conduction of cardiac action potential
What does the P-wave represent?
Atrial depolarization
What does the QRS complex represent?
Ventricular depolarization
What does the T wave represent?
Ventricular repolarization
Five large boxes on the ECG graph represent how much time?
1 second
What represents one full wave on an ECG?
1 R-R interval
What is the rate (beats/min) equation equal to?
Rate = 60 (sec/min) / R-R interval (sec/beat)
What is the 2nd rate equation that can also be used involving the number of boxes in each R-R interval?
Rate = 300 / # of boxes in each R-R interval
Where is the heart’s pacemaker and what is it?
The SA node in the right atrium
What happens once the SA node is activated?
The atria depolarize and contract. Meanwhile, the stimulus arrives at and stimulates the AV node to fire.
The rhythm set by the SA and AV nodes in pacing th heart is called?
Normal sinus rhythm.
What does the PR interval represent?
It tells us how long it takes the action potential to conduct through the AV node before activating the ventricles.
What does the P-wave duration tell us?
How long atrial depolarization takes
What does the duration of the QRS complex tell us?
How long it takes for the depolarization to spread throughout the ventricles.
What does the QT interval represent?
How long the ventricles stay depolarized. Also a measure of the ventricular action potential.
What happens to the QT interval as heart rate increases?
It gets shorter
The normal axis of ventricular depolarization in the frontal plane lies between what 2 angles?
-30 degrees and +90 degrees
What can change the axis of ventricular depolarization?
- Hypertrophy of one or both of the ventricular walls
2. Conduction blocks in one or several of the ventricular conducting pathways
What are the 2 methods to which we can measure the axis of a wave within the frontal plane?
- Geometric method
2. Inspection method
Which is the more accurate method in measuring the axis of a wave within the frontal plane?
The Geometric Method
Which is the quicker and easier method used by clinicians in measuring the axis of a wave within the frontal plane?
The Inspection Method
